Easy access to the embryo makes Xenopus laevis an excellent model for studying the earliest stages of nervous system development. Preliminary studies using a voltage-sensitive dye and electrophysiology revealed that differentiating Xenopus spinal neurons in culture undergo slow spontaneous voltage transients (SVTs) that can last on the order of minutes. I aim to characterize SVTs with regard to changes in duration, frequency (transients/hr), magnitude, and ionic dependence as the neurons differentiate. I will also attempt to identify the mechanisms by which these transients are generated by assessing the effects of activation or blockade of second messenger cascades. The studies above will be accomplished using both optical and electrophysiological techniques in vitro and in vivo. This is a novel form of activity, and the many studies demonstrating a critical role for activity in development provides strong motivation for the experiments proposed.